A position sensing device is a mechanism that is capable of producing a signal in response to being oriented by gravity with respect to the center of the earth. Typical position sensing devices, including reed switches and mercury switches, are undesirable due to problems inherent in their construction. For example, reed switches with sliding magnet actuators provide inaccurate outputs in humid operating conditions. Switches where mercury is used as a sliding conductor are also undesirable because they require the use of mercury, which is a toxic substance. In today's environment conscious atmosphere and mentality, the elimination of mercury switches eases disposal and other problems associated with the handling of toxic substances.
Another position sensing device, disclosed in a pending patent application Ser. No. 07/309,451, filed on Feb. 10, 1989, and titled "Position-Sensitive Educational Product," uses a single conductive ball enclosed within a hollow tube with a metal contact on one end. When the ball rolls to the end of the tube and touches the metal contact due to the orientation of the device with respect to the center of the earth, an electrical signal is produced. Although the structure of the single ball position sensor is relatively simple and economical to manufacture, it is inherently unreliable. The unreliability and inaccuracy of the sensor is grounded in the fact that the electrical signal is produced by the ball touching the metal contact only at one point and touching the tube only at one point. The electrical signal produced is noisy as a result.
In the particular application of children's toys, it is often desirable to determine the position or orientation of the toy so that a correlative auditory or visual response to a child's manipulation of the toy may be appropriately displayed. For example, a doll may emit crying sounds when it is laid down and giggling sounds when it is picked up. A more sophisticated example may consist of an object having multiple surfaces, where a pictorial representation of animals, for example, is depicted on each surface. Whenever the object is set in motion and comes to rest with a surface in the up position, the object may announce the name of the animal and emit an auditory representation of the depicted animal shown on the upwardly facing surface, for example. The multiple surface educational toy is described in detail in aforementioned pending patent application Ser. No. 07/309,451. In the children's toy environment, additional consideration to ensure accurate and safe operation of the toy in view of possible adverse operating conditions, such as shock, vibration and moisture, is especially important.
Therefore, a need has arisen to provide a position sensor that is structurally simple, economical to manufacture and does not involve the use of toxic substances. The desirable position sensor must have the capability to produce a relatively clean electrical signal that is indicative of its orientation with respective to the center of the earth. Furthermore, the desirable position sensor must retain its accuracy in an adverse environment.